Chris,

I think that precaution is redundant... when you start your robot there is ripple when start the ON switch, and your uP works after that. When the charger goes on, I dont think that you'll have a ripple more dangerous than when you started the robot... BUT a capacitor is always good for filtering that noise... the diodes? Dunno, but I don't think that you'll have a power spike going from positive to negative... don't you have a osciloscope to see what happens when you start the charger in parallel with a battery and a load???
HTH
orlando